The invention relates generally to load measuring apparatus and more specifically to a load measuring apparatus incorporating a load cell and a plurality of interleaved plates and pivots which eliminate sensitivity to transverse forces and ensure accurate load measurement in vehicle scales and similar applications.
Weight measurement of vehicles to ensure that they are not in violation of prescribed highway load limits, to measure the amount of bulk goods charged and delivered by a vendor or both requires scales that have not only an exceptionally large capacity but which are also exceptionally accurate. In the last several decades, the technology of vehicle weighing apparatus has shifted from modified and complex balance beam type mechanisms to multiple load cell configurations in which multiple measurements are appropriately summed and provided by electronic components. U.S. Pat. Nos. 3,266,584 to Lee, 3,533,481 to Paelian, 3,831,441 to Petty and 4,281,728 to Dickason et al. present various weighing devices utilizing load cells.
One of the concerns often addressed in the prior art relating to large scales such as truck scales is an unwanted and undesirable sensitivity to loads and forces directed in anything other than a purely vertical direction. Such sensitivity results from oblique forces that, through the scale platform suspension system, resolve into a vertical and horizontal component, the vertical component either subtracting from or more commonly adding to the actual vehicle weight. The problem, of course, is not unique to large vehicle scales but due to the size of the platform and the unavoidability of utilizing multiple point suspension configurations, the problem is much more significant than in smaller weighing apparatus of lesser capacity.
U.S. Pat. No. 2,793,851 to Ruge discloses an early load cell assembly which addresses this problem. It includes spherical upper and lower ends on the load sensing and transfer members which are intended to cause it to align with and respond only to vertically directed loads. This same problem is addressed in U.S. Pat. No. 3,407,891 to Weigand wherein a compression type load cell and its associated load transfer member include a plurality of pairs of curved surfaces and complementary engaging members which likewise are intended to eliminate measurement of transverse forces by rendering the associated load cell insensitive to them.
U.S. Pat. No. 4,248,317 to Rahav discloses another load cell assembly wherein curved upper and lower surfaces are intended to permit movement and alignment of the load cell along the vertical force line and thereby render it insensitive to horizontal or oblique forces.
U.S. Pat. No. 4,627,507 to Powell et al. teaches a load cell assembly wherein the load cell is placed in compression. The load cell senses the weight which is transferred through a pair of parallel links which are loaded by pairs of upper and lower parallel pins. Here, too, the intention it to render the load cell insensitive to loads directed along other than vertical lines of action.
As noted, several of the foregoing patents disclose weighing apparatus wherein the load cell is placed in compression to weigh a vehicle or other object. However, it is generally acknowledged that such operational mode is more sensitive to the concomitant undesirable measurement of transverse and oblique forces. The alternative comprehends placing the load carrying members and specifically the load cells in tension. However, the mechanical components of such an arrangement are generally more complex than a weighing platform which places the load cells in compression. Furthermore, the vertical height of such a platform is generally greater than that of a platform which weighs and operates in compression. Thus, it is apparent that improvements directed to vehicle and platform scales which weigh with load cells placed in tension, which are insensitive to oblique loads and forces and which occupy only minimal vertical distances are not only desirable but also possible.